1. Field of the Invention
The present invention relates to digital video play apparatuses and more specifically to an apparatus and method for controlling bit rates of a digital video stream in a reverse play operation.
2. Description of the Related Art
Generally, Moving Picture Experts Group (MPEG) digital video play apparatuses receive a digital video stream from digital storage media (DSM), such as digital versatile discs (DVDs), digital video cassette recorders (DVCRs), and hard disk drives (HDDs), in order to play the digital video stream or perform various trick-play functions. Trick-play functions may include a fast forward, a slow forward, a fast reverse, and a slow reverse.
The types of picture that may be found in a MPEG display stream include an intra-coded picture (I-picture), a predictive-coded picture (P-picture), and a bidirectionally predictive-coded picture (B-picture). The I-picture may be encoded by a discrete cosine transform (DCT) without using motion compensation. The P-picture may be encoded by performing motion compensation on the basis of an I-picture or another P-picture and then applying a DCT to the remainder. B-pictures may be processed different from P-pictures with respect to motion compensation. For a B-picture, two frames one before and one after a current frame may be used.
In MPEG-2 standards, a picture sequence has a structure of I, B, B, P, B, B, . . . , P, B, B, etc. A first I-picture to a picture prior to a next I-picture is referred to as a group of pictures (GOP). In addition, if a number of pictures in the GOP may be defined as “N”, a number of pictures between I- and P-pictures or between P- and P-pictures (i.e., a picture period) may be defined as “M.” N and M may be variable in one video sequence. If a picture period of any GOP is, for example, three, the picture sequence may have a structure of I, B, B, P, B, B, P, B, B . . . . If a picture period is two, the picture sequence may have a structure of I, B, P, B, . . . where the number of pictures also varies.
Various problems may arise due to a difficulty of identifying accurate information from the group of pictures of a digital video stream during reverse play (fast or slow), because the GOP may have a varying structure with respect to a type, a period and a number of the pictures.
General video play apparatuses do not necessarily use an I-frame encoder due to their complex construction. Instead, the video play apparatuses may store raw data in a memory unit to use in a reverse play which may require more and/or larger memory units.